Piston rings are open-ended rings which fit into a groove on the outer diameter of a piston of an internal combustion motor.
Piston rings are expected to fulfill a lot of severe demands.
First of all piston rings must provide a seal between the piston and the cylinder wall.
Secondly piston rings must minimize the blow-by, i.e. the amount of combustion gas that seeps the piston rings.
Thirdly piston rings must harness the full power of the combustion stroke.
As a fourth requirement, piston rings must scrape off the oil from the cylinders in order to prevent contamination of the combustion process.
A fifth requirement is that the piston ring must regulate the heat transfer from the piston to the cylinder wall.
As a sixth requirement the piston ring must control the thermal changes in the engine.
A seventh requirement is that the piston ring must regulate the oil consumption of the internal combustion motor.
Having regards to these different requirements, the design of a piston ring is driven by several demands which may be often contradictory. Some of these demands are reduced oil consumption, lower friction, higher power output, longer life, decreased variability, reduced exhaust emissions and low cost.
Existing piston ring designs originate from standards developed by engine and ring manufacturers based on tests and data gathered over a very long period of time. Piston ring properties are chosen utilizing a particular combination of the piston ring material, the coating on the piston ring, and the geometry of the piston ring.
The present invention relates to the coating aspect on the piston ring.
Prior art documents U.S. Pat. No. 6,142,481, U.S. Pat. No. 6,279,913 and DE-U1-296 05 666 all disclose various diamond-like carbon coatings on piston rings.
The present invention provides an alternative coating giving an improvement over existing diamond-like carbon coatings on piston rings, more particularly with respect to reduction of friction and to surface coverage and corrosion protection.